Early-type dwarf galaxies with multicomponent stellar structure: Are they remnants of disc galaxies strongly transformed by their environment?

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
e-mail: jalfonso@iac.es
² Universidad de La Laguna, Dept. Astrofísica, 38206 La Laguna, Tenerife, Spain

Received: 16 July 2015
Accepted: 19 January 2016

Abstract

Context. The surface brightness distribution of ~30–40% of the early-type dwarf galaxies with − 18 ≤ M_B ≤ −15 in the Virgo and the Coma clusters is fitted by models that include two structural components (Sérsic + exponential) as for bright disc galaxies.

Aims. The goal of the present study is to determine whether early-type dwarf galaxies with a two-component stellar structure in the Virgo and the Coma clusters are low-luminosity copies of bright disc galaxies or are the remnants of bright galaxies strongly transformed by cluster environmental effects.

Methods. I analysed the location of bright disc galaxies and early-type dwarfs in the r_b,e/h– n plane. The location in this plane of the two-component dwarf galaxies was compared with the remnants of tidally disrupted disc galaxies reported by numerical simulations.

Results. Bright unbarred disc galaxies show a strong correlation in the r_b,e/h–n plane. Galaxies with larger Sérsic shape parameters show a higher r_b,e/h ratio. In contrast, two-component early-type dwarf galaxies do not follow the same correlation. A fraction (~55%) of them are located outside the locus defined in this plane by having 95% of bright disc galaxies. This distribution indicates that they are not a low-mass replica of bright disc galaxies. The different location in the r_b,e/h– n plane of two-component early-type dwarfs and bright galaxies can be qualitatively explain whether the former are remnants of disc galaxies strongly transformed by tidal processes.

Conclusions. The progenitors of ~20−25% of early-type dwarf galaxies with − 18 ≤ M_B ≤ −15 in the Virgo and Coma clusters could be bright disc galaxies transformed by effects of the environment. These tidally transformed galaxies can be selected according to their location in the r_b,e/h–n plane.